The present invention relates to a semiconductor device, a battery pack, and a mobile terminal.
Among the CPUs (Central Processing Units) in an internal circuit installed in mobile terminals such as notebook computers, there is a type of CPU that has a function of changing its operating frequency (hereinafter called “variable frequency function”) in order to keep a balance among the power consumption, the calculation performance, and the reliability (life span). A CPU having the variable frequency function lowers the clock frequency (normal clock operation) in the normal operation state, and thereby prevents the increase of the power consumption, and/or maintains the CPU at a low temperature and thereby prevents the deterioration in the reliability. On the other hand, when the resource request from the application(s) increases, the CPU having the variable frequency function raises the clock frequency (high-speed clock operation) and thereby increases the calculation performance.
Note that when a CPU having a variable frequency function is driven by electric power supplied from an assembled battery in which a plurality of secondary battery cells are combined, the period of the high-speed clock operation and the clock frequency in the high-speed clock operation state are determined based on the amount of the electric power that can be output from a battery. For example, this CPU is formed so as to be able to select a plurality of clock frequencies higher than the clock frequency in the normal clock operation state as a clock frequency in the high-speed clock operation state, and the optimal clock frequency is selected based on the amount of the electric power that can be output from the battery at this time.
Meanwhile, the state of a battery implemented in a mobile terminal such as a notebook computer is monitored by a battery monitoring system accommodated in a battery pack together with the battery. The battery monitoring system typically includes a battery control IC (FGIC: Fuel Gauge IC), a sense resistance to detect charging and discharging currents of the battery as voltage information, a charge controlling MOS transistor, a discharge controlling MOS transistor, and a protection circuit such as a thermistor or a fuse. The battery control IC is formed to include, for example, a microcontroller, and achieves a battery remaining capacity management function, a function of controlling the charge controlling/discharge controlling MOS transistors, and a function of protecting the battery. The battery control IC generates information indicating the state of the battery based on the results of detecting the battery voltage and the charging and discharging currents of the battery to notify the internal circuit of the mobile terminal of the information. The information indicating the state of the battery includes, for example, a full charge capacity (FCC), a remaining capacity (RC) of the battery, and a state of charge (SOC) of the battery. Related techniques are disclosed in Japanese Unexamined Patent Application Publication Nos. 2010-34016, 2003-79059, and 2001-51029.
The battery control IC generates, in addition to the information indicating the battery state described above, information of a maximum power amount that can be supplied from the battery to the internal circuit based on the results of measuring the battery voltage and the discharge current of the battery. The information of the maximum power amount is notified as needed (e.g., once every second) to a PC system (internal circuit) of the notebook computer, and is used to determine the period of the high-speed clock operation and the clock frequency in the high-speed clock operation.